fix: warning when building macOS arm64 wheels

When `MACOSX_DEPLOYMENT_TARGET` is not set by the user, cibuildwheel always defaults to `10.9`.
This leads to warning when building arm64 wheels.
This commit removes the warning by setting the default to `11.0` for arm64 builds.

test/test_macos_archs.py

@@ -66,11 +66,15 @@ def test_cross_compiled_test(tmp_path, capfd, build_universal2):
             "CIBW_BUILD": "cp39-*",
             "CIBW_TEST_COMMAND": '''python -c "import platform; print('running tests on ' + platform.machine())"''',
             "CIBW_ARCHS": "universal2" if build_universal2 else "x86_64 arm64",
+            "CIBW_BUILD_VERBOSITY": "3",
         },
     )
 
     captured = capfd.readouterr()
 
+    assert "[WARNING] MACOSX_DEPLOYMENT_TARGET is set to a lower value" not in captured.out
+    assert "[WARNING] MACOSX_DEPLOYMENT_TARGET is set to a lower value" not in captured.err
+
     if platform.machine() == "x86_64":
         # ensure that tests were run on only x86_64
         assert "running tests on x86_64" in captured.out